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Antibiotic Sensitivity Test

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Antibiotic Sensitivity Test Introduction Antibiotics are used to treat bacterial infections. They either kill the bacteria or prevent them from multiplying. They do not however have any effect on viruses. The first antibiotic was discovered accidentally in 1928 by a Doctor Sir Alexander Fleming. He left the lid of a petri dish and discovered some unusual fungus growing in it. He noticed that where the fungus grew the bacteria had ceased to exist. He reasoned that fungus must kill the bacteria and identified the substance as Penicillium notatum. It wasn't until 1940 that Howard Florey discovered a way to make the drug useful for humans. The majority of antibiotics that we use today are natural products that are made in large quantities in enormous vats by fermentation, there are however some antibiotics which are made synthetically. Aim The aim of the experiment was to test the effect of eight antibiotics on the bacterium Staphylococcus albus. ...read more.


Allow the nutrient agar to cool and set. Step 4 Once set, using a sterile pair of forceps, place the Mastring disk onto the set agar and replace the lid. The Mastring disk is a paper disk with 8 coloured disks attached to it. These 8 disks are impregnated with a known antibiotic. (See Picture 1 below) Picture 1 Photo of Mastring being used in Antibiotic Sensitivity Test Control Dish 2 An identical dish was set up using steps 1-3 as above. This will be a control dish to compare S. albus growth with and without antibiotics present. Control Dish 3 A third dish containing 25cm of sterile nutrient agar only was set up also as a control. This control will check that the agar was sterile and that the aseptic technique was carried out correctly. Once the agar had set in all 3 petri-dishes, seal with tape and turn upside down to prevent condensation forming on the plates and incubated for 48 hours at 25C. ...read more.


Conclusion The most effective antibiotic to inhibit S. albus was Tetracycline as the clear area was very well defined. Some of the other antibiotics were not as effective, the clear area was not so well defined and in some cases the areas overlapped and made it difficult to measure there effect accurately. The result did support the hypothesis. Control Dish 2 was cloudy in appearance, which indicated a uniform growth of S. albus, throughout the agar. This suggests that the agar had been prepared correctly to enable the growth of the bacteria. (See diagram 5) Control Dish 3 was completely clear, which indicated no growth of micro organisms and that the aseptic technique was carried out correctly. (See diagram 5) Further Work A different bacterium could be used to observe whether the same antibiotic was as effective as on the S. albus. The same bacteria could be used but isolated with just one antibiotic to get a clearer result. ...read more.

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